Bionic Broomstick
*flashback to the days of building balsa gliders*
Putting a fabric covering over it will improve torsional stiffness by quite a bit. My old kits had a forward spar, so three rows of spars, which may have improved stiffness.
I am loving this build, skip.
I’m dying to see how your linkages are going to work. In my meager musings on the subject, it seems like flex in the system can effect the trim of the tailplane (and maybe the flap).
That’s my worry about feathering in strong winds—that flex in the system will cause the wing to go “on” when you want it to stay off.
chris
*flashback to the days of building balsa gliders*
Putting a fabric covering over it will improve torsional stiffness by quite a bit. My old kits had a forward spar, so three rows of spars, which may have improved stiffness.
Remember it well, peeled a lot of ambroid off my fingers..
After dry fitting a piece of the forward sheeting, 3/16” xps foam, went back and added half ribs in front of the spar, feel a lot better about it now.
I am loving this build, skip.
I’m dying to see how your linkages are going to work. In my meager musings on the subject, it seems like flex in the system can effect the trim of the tailplane (and maybe the flap).
That’s my worry about feathering in strong winds—that flex in the system will cause the wing to go “on” when you want it to stay off.
I’m enjoying it also, haven’t been this excited about boat design ramifications since my early Safari days.
It’s true that the “tail bone is connected to the flap bone” but since pivots are relatively forward any flex “should” just feather things more. Don’t have the numbers in front of me but the designed tail volume coefficient is fairly conservative.
The big question in my mind is how’s the thing going to work in light winds? It’s slam dunk easy to make things work in moderate conditions, heavier stuff is probably mainly an engineering exercise. But if the real world lift coefficient is 2X or better than a good soft sail (Elkhaim’s thesis says 3X) we have a potential winner.
If it only takes half as much area to match a good soft sail in light winds the wingsail runs away in positives beyond that. But if it takes just as much area would be hard to justify the effort. This is all in the realm of easy cruising, the racers have a whole different set of criteria.
Finding out some of the answers along with whatever additional questions are lurking really is fun.
Skip
Regarding the half ribs; it looks to me like you have the full ribs at maybe 16” centers? So the new halves are on 8” centers?
The big question in my mind is how’s the thing going to work in light winds? It’s slam dunk easy to make things work in moderate conditions, heavier stuff is probably mainly an engineering exercise. But if the real world lift coefficient is 2X or better than a good soft sail (Elkhaim’s thesis says 3X) we have a potential winner.
You’re certainly pushing all the right “light wind” buttons with that section! I can’t find in Wilkaim’s site whether he was happy with the section+flap in light wind. He was happy overall, but did it work as he’d hoped in the light?
If it only takes half as much area to match a good soft sail in light winds the wingsail runs away in positives beyond that. But if it takes just as much area would be hard to justify the effort. This is all in the realm of easy cruising, the racers have a whole different set of criteria.
I’m totally with you on this, Skip. Waiting with bated breath!
Talk to me, please, about the big PVC clamps you’re using? Looks like they came out of maybe 8” diameter pipe? What kind of clamping pressure do you get from these? Maybe at 1”, also 2” spread? Roughly what did they cost, apiece? (comparing them to a 3” - 4” C-clamp from Harbor Freight) Thanks!
Dave
Regarding the half ribs; it looks to me like you have the full ribs at maybe 16” centers? So the new halves are on 8” centers?
Close 10” & 5”
You’re certainly pushing all the right “light wind” buttons with that section! I can’t find in Wilkaim’s site whether he was happy with the section+flap in light wind. He was happy overall, but did it work as he’d hoped in the light?
Good question, as I understand it, he didn’t actually use the flap for much of the trials, partially because of structural deficiencies in the wing panel joins, plus there was a lot invested in the whole setup, not a consideration in my build 😉
If it only takes half as much area to match a good soft sail in light winds the wingsail runs away in positives beyond that. But if it takes just as much area would be hard to justify the effort. This is all in the realm of easy cruising, the racers have a whole different set of criteria.
I’m totally with you on this, Skip. Waiting with bated breath!
Thanks
Talk to me, please, about the big PVC clamps you’re using? Looks like they came out of maybe 8” diameter pipe? What kind of clamping pressure do you get from these? Maybe at 1”, also 2” spread? Roughly what did they cost, apiece? (comparing them to a 3” - 4” C-clamp from Harbor Freight) Thanks!
6” PVC, no cost except for the electricity to cut them, pipe was jobsite scrap, normally 4” is the best for clamping wood bits, accepted cost is 25 cents each, 6” are for light pressure things like foam bits. If you’re considering substitution for C-clamp figure on 2-3 times as many clamps.
Update on the wing.
The wing currently weighs 8.5# does not include covering (nominal) trailing edge flap or tail surface/booms.
I think everything will hold together for what I have in mind, no heavy wind testing contemplated.
It’s possible to tilt the rig over and slide the wing on, but an extra set of hands and eyes would be helpful. There’s a little slop in the top bearing but overall seems OK. The wing will rotate thru about 360 degrees if tail is pushed fairly hard so frictions not too bad, no silicone/teflon spray applied yet.
Skip
Another picture.
The foot pedals should be easy to implement, the only problem is I’m running out of scrap ply, may need to make the pedals out of my small stash of ACM (aluminum composite material, fairly light and stiff, the stuff used on gas station canopies and such).
Skip,
It looks really good and promising.
Keep us posted!
Laurent
Great work skip!
It’s possible to tilt the rig over and slide the wing on, but an extra set of hands and eyes would be helpful.
Skip
Would a little wheeled dolly which you could mount (temporarily) to the top of the wing help ? You could spend your time at the bottom of the wing guiding it on to the mast. Then you could use it when launching BB :o)
It’s looking fantastic, Skip. Everything so functional but still well proportioned. A real Bauhausboat…
Thanks for keeping us posted.
Would a little wheeled dolly which you could mount (temporarily) to the top of the wing help ? You could spend your time at the bottom of the wing guiding it on to the mast. Then you could use it when launching BB :o)
Probably not, the wing is plenty light enough and the whole boat is easy to move by hand, is going to be several pounds lighter with the wing.
Process right now is to tilt the boat on its side with the stub mast projecting out at about 30 degrees from the horizontal. It’s tricky at the moment because that’s about at a balance point, boat wants to fall forward or back depending on how the wing is interacting with the stub mast. I’d like someone there to help ‘hold the boat’ AND guide the cam follower over the cam. The top of the cam is beveled but still would be nice to have an extra pair of eyes on the deal, follower wasn’t installed for first trials.
Right now its easy to hold the wing by the leading edge and trailing edge, the trailing edge option goes away when the wing is covered and tail flap installed. The plan is to hold the wing by the lower tail boom and forward facing counterweight shaft and balance the wing on my head at the D spar.
Will know in a couple of weeks.
Thanks to all for comments
Skip
Update, wing is completed (I think) assembled on boat, Susie helped the wing with tail boom awkward to get out from under house. Plan is to take boat to Lake Somerville on Tuesday, John Wright to meet us at lake. Susie will stay long enough to take some pictures, John and I will probably spend most of the day.
Currently the wing assembly has throws for rudder and flap set as low as they will go in this blind iteration. Plan is to increase rudder throw if needed, possibly flaps later. Everything seems pretty well behaved, wing swings around as needed in the fluky breeze in the trees. Both foot pedals and tail control cables need some attention, spectra is low stretch not no stretch. Only major building error is eyeball construction on flap control arms left the top flap section out of line by a degree or two. Also discovered that H.F. metal epoxy is no substitute for JB weld.
Disassembly was done solo and I discovered it was important to to get the brace block up on the tripod rather than the hull. I think it may be better to assemble the tail booms and rudder once the wing is on and still laying on its side.
More in a few days, I’m hoping the wind is a little lighter than predicted but will see on Tuesday.
Skip
More pictures
Looks great Skip! Fast work too.
Do you have a counterweight on the wing?
Mal.